Pong, while not the first videogame, was the first coin-op arcade game and the first mainstream videogame that was available to almost everyone. The origins of Pong lie with an abstract tennis game created with an old oscilloscope and some vacuum tubes by Willy Higinbotham way back in 1958. What eventually became "Pong" was a pretty simple game with simple rules - hit the ball across the playing field and try your best to hit it past your opponents paddle on the other side.

Use your mouse to guide your paddle up and down.

(Source: http://www.widgetbox.com/widget/pong)